The present disclosure relates to a fixing device and an image forming apparatus provided with the same.
Conventionally, as apparatuses for forming (printing) an image on paper as a recording medium, image forming apparatuses such as a copy machine, a printer, a facsimile machine, and a multi-functional peripheral having functions thereof have been known. In an image forming apparatus, processes described below sequentially perform: a charging step of charging a surface of a photoreceptor drum; an exposure step of forming an electrostatic latent image on the surface of the photoreceptor drum by causing laser light to emit on the charged surface of the photoreceptor drum; a development step that develops an image by depositing toner on the electrostatic latent image formed on the surface of the photoreceptor drum; an image transfer step that transfers a toner image formed of the toner deposited on the surface of the photoreceptor drum to the paper; and a fixation step that fixes the toner image transferred to the paper. An image is thus formed on the paper.
Among the abovementioned steps, in the fixation step, the toner needs to be heated and fused in order to fix the toner composing the toner image transferred to the paper. As a fixing device that performs the fixation step, a fixing device has been conventionally used, which includes: a heating rotator; a pressurizing rotator that nips the paper on which the toner image is transferred to form a fixing nip with the heating rotator; and a heater such as a halogen lamp for heating the heating rotator.
As a method of heating a heating rotator of a fixing device, heating a heating rotator by Induction Heating (IH) using electromagnetic induction has been recently used, in addition to a method of heating by a halogen lamp. In the induction heating (IH) method, the fixing device is provided with: an induction coil that generates a magnetic flux by an applied current; a heating rotator that is disposed in a region through which the magnetic flux generated by the induction coil passes; a pressurizing rotator that is disposed to face the heating rotator; and a magnetic core unit configured to form a magnetic path passing inside an inner peripheral edge and outside an outer peripheral edge of the induction coil such that the magnetic path circularly encloses the induction coil. The magnetic core unit includes, for example, a plurality of arch core portions and a core supporting member that supports the arch core portions. The arch core portions have an arch shape facing an outer surface of the heating rotator with the induction coil being interposed therebetween. The fixing device employing the induction heating (IH) method has advantages of more rapid heating and higher heating efficiency over the fixing device employing the heating method using a halogen lamp.
In such a fixing device, an amount of heat generated by the heating rotator is proportional to an amount of magnetic flux passing through the heating rotator. The amount of magnetic flux passing through the heating rotator varies according to positional relationships of the induction coil and the arch core portions of the magnetic core unit with respect to the heating rotator.
Given this, when a distance between the heating rotator and the induction coil, and a distance between the heating rotator and the arch core portions are not constant, the heating rotator may not be able to generate a predetermined amount of heat.
On the other hand, it is not easy to ensure dimensional accuracy of the arch core portions due to the difficulty related to a manufacturing technique and it may be likely that a dimensional error often occurs. In order to absorb the dimensional error, special support equipment has been used for assembling (fixing) the core supporting member and the arch core portions, or a gap has been provided between the core supporting member and the arch core portions and filled with an adhesive for bonding the core supporting member and the arch core portions. Accordingly, it has not been easy to assemble (fix) the core supporting member and the arch core portions.